The invention relates to a crane, in particular a mobile wharf crane.
German patent application DE 10 2004 010 988 A1 discloses a hybrid drive system for a straddle carrier. Such straddle carriers are used in seaports and container terminals for transporting and stacking containers. The hybrid drive system includes a current generating unit having a diesel motor which drives the three-phase generator. The three-phase generator supplies, via a rectifier, a DC voltage intermediate circuit to which traction, lifting and auxiliary motors are connected via inverters. In order to, design the current generating unit in a considerably smaller and simpler manner, a short-term energy store is connected to the DC voltage intermediate circuit via a charge/discharge regulator in order to cover short-term peaks in energy requirement such as those produced when driving and braking the traction drive of the straddle carrier or when lifting and lowering the containers. This short-term store can be charged when braking the traction and lifting drives in a generator-based manner and therefore the energy supplied back into the DC voltage intermediate circuit by the traction and lifting drives does not need to be converted into heat using break resistors. The short-term store thus eliminates these energy losses and is used as an intermediate store for the energy. The short-term energy store is formed from double-layer capacitors which are connected together, have extremely high capacitances and are also known as “ultra capacitors” or “Ultra-Caps”. In addition to the short-term energy store, a further energy store is connected to the DC voltage intermediate circuit via a further charge/discharge regulator. The further energy store is formed as a lightweight high-energy battery, in particular sodium chloride, nickel, sodium-sulphur or nickel-metal hydride storage batteries, in order to cover average peaks in power requirement which are produced for example for journeys of a few minutes. The charge/discharge regulator for the short-term energy store and the further energy store is formed as an adjustable two-quadrant DC/DC converter. Further, an electric controller is provided which is connected to the current generating unit, to the short-term energy store and to the further energy store in order control these depending upon the operating state of the hybrid drive system.
U.S. Pat. No. 7,554,278 B2 discloses a hybrid drive system of a crane with rubber tyres and having on the input-side a DC voltage circuit which is supplied with electrical energy on the one hand by a three-phase generator, driven by an internal combustion engine, having a rectifier disposed downstream, and on the other hand by a battery unit, used as an energy store system. In order to supply the electrically operated crane drive motors with energy, an AC voltage circuit is also provided by means of which all of the crane drives, in particular a lifting drive, are electrically connected. A further switching circuit is also provided which can be connected to the DC voltage circuit and via which the electrical energy recuperated e.g., when lowering a load by braking the lifting drive in a generator-based manner can be supplied into the battery unit of the energy store system for charging same.
Furthermore, so-called mobile wharf cranes are known from the current company brochure from Gottwald Port Technology GmbH, Dusseldorf, Germany, entitled “Hafenkran—Modell 4” (“wharf crane—model 4”), by means of which containers or bulk material are handled in seaports or container terminals. Such a mobile wharf crane consists substantially of a lower carriage, by means of which the mobile wharf crane is supported on land, e.g., on a quay, or on a floating pontoon, and an upper carriage which is mounted on the lower carriage so as to be rotatable about a vertical axis. The lower carriage can travel on the quay via tyres or on rails via rail wheels. During the handling operation, the lower carriage is supported via stanchions. Disposed on the upper carriage are a vertically extending tower, the rotating and lifting mechanisms for the rotation of the upper carriage and the lifting of a load, and a counterweight. Further, a jib is articulated on the tower approximately in the region of half of its length and on the side remote from the counterweight. The jib is connected to the tower so as to be pivotable about a horizontal luffing axis and can also be pivoted out of its laterally projecting operating position into an upright rest position via a luffing cylinder articulated on the jib and at the bottom on the upper carriage. Moreover, the jib is conventionally formed as a lattice boom.
In relation to their drive design, such mobile wharf cranes have the configuration of a serial hybrid system since they operate with a diesel-electric drive in which the chemical energy of the diesel fuel is converted into mechanical work by an internal combustion engine and is supplied as electrical energy by a three-phase generator to an AC voltage circuit. For driving the lifting mechanism, the rotating mechanism and the luffing mechanism as well as any other drives, DC current motors or three-phase motors are used in which a new conversion of the electrical energy back into mechanical work takes place, which is finally used to lift loads, move and rotate the crane or move the jib. Energy which is supplied back into the AC voltage circuit e.g., by lowering loads on the jib, is initially made available to the remaining consumers. As soon as there is excess energy in the AC voltage circuit, this is converted into heat by brake resistors, wherein the energy supplied back is eliminated, i.e., is ultimately lost.